Ovarian cysts are fluid-filled pockets or sacs within or on the surface of an ovary. They are quite common. In fact, the ovaries normally grow cyst-like structures each month as an egg develops. When these normal monthly cysts persist or keep growing, they are known as functional cysts because they occur in women of childbearing age and originate during the normal function of the menstrual cycle. Two types are especially frequent: follicular cyst and corpus luteum cyst. These are linked with the monthly cycle of ovulation. Another benign condition, polycystic ovarian syndrome involves the growth of numerous cysts, usually on both ovaries, and is unrelated to the monthly cycle. Fimbrial cysts are on the "fingers" or flaps of the fallopian tube closest to the ovary. Both fimbrial cysts and ovarian cysts may indicate an early cancerous (tumour) condition.